A collection of computer systems and programming tips that you may find useful.
 
Brought to you by Craic Computing LLC, a bioinformatics consulting company.

Friday, April 5, 2013

Fixing incorrect timezones in Ruby

Timezones can be tricky to manage and sometimes I just get them wrong - like now...

I had been parsing strings representing local times in Seattle and then storing these without an explicit timezone on a machine which uses UTC by default - so they got stored as that time in UTC (not converted to UTC - the exact time string in UTC.

For example: Fri, 05 Apr 2013 14:24:39 (the local time in Seattle) was stored as Fri, 05 Apr 2013 14:24:39 UTC +00:00 which is 7 hours earlier than it should be.

The easiest way to fix this, that I found is to convert back to a string, strip of any record of a timezone and then parse it back into a time, having temporarily set the TZ environment variable to the correct local timezone.

NOTE that this works on UNIX/Mac OS X systems - not sure about Windows...

puts ENV['TZ']         => nil
puts t                 => 2013-04-05 14:24:39 UTC
s = t.to_s
puts s                 => "2013-04-05 14:24:39 UTC"
s.sub!(/\s+UTC/, '')
puts s                 => "2013-04-05 14:24:39"
ENV['TZ'] = 'US/Pacific'
t1 = Time.parse(s)
ENV['TZ'] = nil
puts t1                => 2013-04-05 14:24:39 -0700

Remember to reset the TZ environment variable back to nil

Be very careful about using gmtime and localtime as these methods operate in place. So ALWAYS make a copy of your time before applying those conversions

t            => 2013-04-05 15:25:41 -0700
t1 = t.dup

t.gmtime     => 2013-04-05 22:25:41 UTC
t            => 2013-04-05 22:25:41 UTC
t1           => 2013-04-05 15:25:41 -0700


1 comment:

Blogger said...

If you want your ex-girlfriend or ex-boyfriend to come crawling back to you on their knees (even if they're dating somebody else now) you have to watch this video
right away...

(VIDEO) Text Your Ex Back?

Archive of Tips